Merc 43L MPI Problems please help

"Hi there,
Im new to this sit

"Hi there,
Im new to this site and i sincerely apologise if this topic has been raised before but i searched and found similar issues but not my exact issue that im hoping someone can help with.. heres my poroblem..

I have a Whittley 660 with a Mercruiser 4.3LMPI. I have 100 hours on the motor and have a serious issue with the motor cutting out at about 3000 to 4000RPM after about 15 minutes. I have taken it to my Mercruiser dealer who has serviced, plugged in computers and continues to tell me that there is NO problem.. However the next day i take it out and it cuts out. I then try to start the motor but nothing. If i raise the trim right up it then seems to start. It will run no problmes as long as i dont increase the REVS. As soon as i do. It cuts out completetly. Starts again after a few turns of the motor but for somereason seems to be linked to the TRIM? Is there a known issue like this? Any suggestions would be great. thank you"

Sounds like a restriction in t

Sounds like a restriction in the exhaust system. Raising the trim raises the exhaust vent closer to the water surface reducing the back pressure. Probable cause is a stuck in closed position of the exhaust "flapper"

"Thanks Bill,
I will pass thi

"Thanks Bill,
I will pass this info onto my so called Mercrusier specialist... thanks again."

"Danny, welcome....

What ye

"Danny, welcome....

What year is the motor? How does the motor behave just as its about to cut out? Is it running as normal, or is it sputtering and coughing, and slowly dying away? Does it stop just like someone turned the key off? Let us know a little more.

Wrench"

Check for water in the fuel fi

Check for water in the fuel filters. Sounds like it could have water accumulating in the float bowl or even fuel starvation at high fuel demand conditions.

"Thanks Wrench,

Pretty sure

"Thanks Wrench,

Pretty sure its not water in the fuel filters as the dealer had already checked this. The year of the motor is a 2004. The motor just simply cuts out. No spluttering, no small power loss, just everything. I dont lose power to the console though. All guages still work and power to the console. I turn the key off and then back on again and try to start but it wont. Let it sit for a bit and raise trim(coincidence or not) then it starts no stumbling. It can idle and as long as i dont give it too much power will stay alive?"

""I turn the key off and t

""I turn the key off and then back on again and try to start but it wont."

It won't what? I turn the key to START and nothing happens? Starter won't turn over the engine? It turns over but plugs won't fire? No spark at the plugs?

It may be a thermal related failure. Internal crack in an ingition related part could be the problem. Use a hair dryer on low heat and fan to heat components while idling. Start w/the coil, ignition amp. module, etc."

"sorry yes, detail is the key

"sorry yes, detail is the key here.... When i turn the key the motor turns but wont fire. Then after a short time and a raise of the trim it fires... and runs smoothly.. The dealer is now telling me its probably the fuel pump?"

"If the dealer wants to change

"If the dealer wants to change the fuel pump, I would try a new pump relay, if equipped, then a pump if the problem persists.

Have them check the wiring connectors to the pump for corrosion or loose connections."

"Just had one of those SENIOR

"Just had one of those SENIOR moments...
A weak coil will run a engine at slow RPM's but will not deliver strong spark at higher RPM's and kill the engine. Sometimes they will start righ up or start after coil cools down. Many times a defective coil will test ok when cold.
The manual should tell you what the resistance should be across the coil termanels. Test it cold then test it when the engine cuts out. If your coil does not meet the specks, replace it."

"I don't think we have det

"I don't think we have determined if it is a spark or fuel problem. The key is in testing when the engine will not start. Have you tested for spark when it wont start??? If there is spark, have you tried priming it to see if it starts on a prime. Have you retested for spark with the trim raised?"